1. Field of the Invention
The present invention is related to a bi-directional DC to DC power converter having a neutral terminal. More particularly, the bi-directional DC to DC power converter having the neutral terminal can be operated in a boost mode or a buck mode to allow a bi-directional electric energy transmission.
2. Description of Related Art
A DC to DC boost/buck power converter with a neutral terminal is often used in power related apparatus. Taking the uninterruptible power supply (UPS) system as an example, a DC to DC boost power converter with a neutral terminal is used to step up an input DC voltage having a neutral terminal to produce an output DC voltage having a neutral terminal with a required level. The output DC voltage having a neutral terminal can be applied to other subsequent devices.
With reference to FIG. 1, U.S. Pat. No. 6,154,380 discloses a conventional boost power converter being composed of an AC power source (U), a full-wave bridge rectifier (100), two inductors (L1, L2), a switch (T1), two diodes (101, 102), two capacitors (C1, C2) and a load.
Electric energy output from the bridge rectifier (100) is temporarily stored in the two inductors (L1, L2) and then transmitted to the two capacitors (C1, C2) to accomplish the voltage boost operation as the switch (T1) is alternately turned on and off. However, the conventional boost power converter has no voltage buck function and only permits the electric energy to be transmitted in one direction. For many applications, a DC to DC power converter integrated with a boost converter mode and a buck converter mode, having a neutral output terminal, and allowing energy being transmitted in two directions to meet requirements of different power systems is necessary.
For a UPS system comprising a single-phase half-bridge inverter and a three-phase four-wire inverter with a split capacitors leg, a battery module of the UPS system has to cooperate with a DC to DC boost power converter to step up voltage and supply two identical DC voltages to the two DC capacitors of the split capacitors leg via a neutral output terminal when the utility system is abnormal. On the contrary, the electric energy must be transmitted in an opposite direction through a DC to DC buck power converter to charge the battery module when the utility system is normal.